Abstract

This paper proposes an intelligent battery health-aware energy management strategy (EMS) for the hybrid electric bus (HEB) with a deep reinforcement learning (DRL) method. Firstly, an EMS based on twin delayed deep deterministic policy gradient (TD3) algorithm considering battery health is innovatively designed to minimize the total operating cost of the HEB. Secondly, the superiority of the proposed EMS over the state-of-the-art deep deterministic policy gradient (DDPG) based strategy is validated. Simulation results show that the proposed EMS accelerates the convergence by 24.00% and reduces the total operating cost by 9.58% compared with the EMS based on DDPG.

Abstract

In order to cope with the environmental problems of climate deterioration, reduce carbon emissions and develop environmentally friendly energy sources without delay. The global energy system is undergoing tremendous changes, accelerating the transformation of the energy structure, and promoting the development of the energy structure to a low-carbon or even carbon-free direction. Renewable energy has received attention due to its clean and green characteristics. Wind power generation, as an important way to develop renewable energy, faces grid security challenges due to the volatility and uncontrollability of wind speed. In this paper, a systematic prediction method is proposed for wind speed: the wind speed sequence is decomposed by the variational modal decomposition method according to the principle of envelope entropy, and the extreme learning machine network optimized by the bat algorithm is used to predict the data after decomposing. Besides, error sequence correction method based on kernel density estimation is proposed to predict residual. The availability of the model proposed in this paper is proved by experiments, and a good prediction effect is obtained. In order to heighten the utilization of wind energy, the wind power dispatching of relevant departments provides a reference method.

Abstract

Quaternary chalcopyrite semiconductors, Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe), have attracted increasing attention for photovoltaics (PV) application in recent years. However, due to the cell architecture borrowed from CuInxGa(1-x)Se2 (CIGS) devices, the open-circuit voltage is the limiting factor preventing further increases in solar cell efficiency. In the present study, band edge energies of Cu2ZnSnS4 and Cu2ZnSnSe4 were analysed electrochemically in order to show band energy alignments of CZTS and CZTSe. The electrochemical steady-state potential windows were also investigated; this provides vital information for various applications of both materials. The valence band energy offset between CZTS and CZTSe was found to be 0.5 eV. Compared with the flat band potential of CdS (-0.8 V vs Ag/AgCl), the open circuit potential in the dark between CZTS and CdS is therefore 0.4 V and 0.9 V for CZTSe. Moreover, from chronoamperometric measurements using an electrochemical field-effect transistor, the conductivity of CZTSe is found to be three orders higher than CZTS, which proves that CZTSe is significantly better for charge transfer.

Abstract

In low permeability reservoirs, poor water injection development effect, high water injection pressure, formation energy can not be effectively supplemented and other problems often lead to unsatisfactory development effect, so it is a big problem to change the development mode to improve oil recovery. The injection of carbon dioxide into the reservoir and geological storage of the injected CO2 can greatly reduce the viscosity of crude oil, improve the fluidity of the oil, and reduce the oil seepage resistance, thus improving the development effect and enhancing the oil recovery. Yesanbo oilfield is located in the south of Dagang oilfield, which is a typical low permeability reservoir. Considering the dual advantages of carbon dioxide geological storage and enhanced oil recovery, this paper chooses this area for reservoir numerical simulation study. Based on the mechanism model, the number of injection Wells, injection velocity, Ratio of vertical to horizontal permeability (Kv/Kh), The influence of critical water saturation value on carbon capture ， utilization and storage (CCUS) scheme operation. The results show that a horizontal well with two straight gas injection Wells is the best. The higher the gas injection rate, the greater the carbon storage and cumulative oil production. When Kv/Kh value increases, the carbon storage decreases, and the cumulative oil production increases. Critical water saturation value increases cumulative oil production and carbon storage decreases. The CCUS scheme constructed in Yesanpu oilfield has dual functions of oil displacement and carbon sequestration, which significantly improves oil recovery and deposits a considerable amount of carbon dioxide into the reservoir. This study provides a scientific basis for the operation of CCUS in the oilfield.

Abstract

The growing energy demand, depleting fossil fuel reserves, and global warming concerns call for a further increase in biomass energy utilization. At present, biomass is mostly used in small-scale applications where the production of electricity is technically and economically disadvantageous. On the other hand, district or communityscale CHP applications with higher efficiencies and lower specific investment costs are a better alternative. Biomass combined heat and power (BCHP) systems can reduce GHG emissions and also have the potential for higher overall energy efficiencies than conventional home heating methods. In this research, an organic Rankine cycle (ORC)-based BCHP for community-scale applications is investigated concerning technical and economic aspects. MDM (Octamethyltrisiloxane) is selected as the ORC working fluid, taking into account the cycle efficiency and system design. The heat of biomass combustion in the boiler is used to vaporize the organic working fluid in the evaporator. The working fluid vapor drives the turbine that spins an alternator. A mathematical model for the community-scale ORC BCHP system is developed to predict its operational performance. Various costs for the BCHP plant are analyzed and the cost of electricity (COE) is calculated. The community-scale or district BCHP plant generates 520.9 kWe electricity with the electrical efficiency reaching 17.24 % at a turbine inlet temperature of 250 °C, and provides hot water with a heating load of 2365.7kWth at a temperature of 79.2 °C. The COE of the BCHP plant is 98.2 $/MWh when not including CO2 credit.

Abstract

A solar-based vapour absorption machine (VAM) chiller-based district cooling system (DCS) has been designed and its financials have been worked out in the context of a high-rise 80 apartment tower. Comparisons have been made with a vapour compression refrigeration (VCR) based DCS, and with the existing system of 3 unitary split air conditioning units per apartment. The solar VAM DCS carbon footprint is 75% and 78 % smaller than VCR DCS and unitary system. While the capital cost is 58 % larger than VCR DCS, the operating costs are 63 % lower. The VAM-based DCS, though practically complex, has the potential for substantial carbon savings which is needed to slow down carbon emissions.

Abstract

Liquid hydrogen is a high-specific-impulse propellant which is widely used in aerospace. Hydrogen storage is a key problem in the long-distance space exploration. In recent years, zero boil-off (ZBO) storage of cryogenic propellants (LH2, LO2, LCH4) is a significant storage technology for space exploration where the cryocooler is used to achieve ZBO. However, it is difficult to achieve the large cooling capacity at 20 K in space. The reverse turbo-Brayton cycle cryocooler has the obvious advantages of large cooling capacity, low vibration, high reliability and long life which is used as the cryocooler in ZBO system. In this study, a reverse turbo-Brayton cycle cryocooler combining nitrogen and helium cycles is designed to provide the cooling capacity at 20 K and 90 K for liquid hydrogen and liquid oxygen. The nitrogen cycle in the system can provide the cooling capacity of 20 W at 90 K for liquid oxygen storage while the helium cycle in the system can provide the cooling capacity of 5 W at 20 K for liquid hydrogen storage. There are three centrifugal compressors and one expander in the nitrogen cycle. The expander is coaxial with the one of compressors which can recover the expansion work. There are four centrifugal compressors and one expander in the helium cycle. A heat exchanger is used to connect the nitrogen cycle and helium cycle. The nitrogen cycle can provide the cooling capacity for the pre-cooling of the helium cycle. In addition, the cryocooler can also provide the cooling capacity of 200 W at 90 K for liquid oxygen and 200 W at 120 K for liquid methane by the nitrogen cycle. The reverse turbo-Brayton cycle cryocooler in this study can achieve the ZBO storage of liquid hydrogen, oxygen and methane in space. This work can provide the theoretical guidance for the design of ZBO storage in the long-distance space exploration.

Abstract

The reduction of waste heat in energy intensive industrial processes in combination with digital technologies will play a key role for the development and decarbonization of modern industrial energy systems. In the last few years, a significant share of the CO2 related to energy was emitted by the industry sector. Since industrial processes often are batch processes, waste heat recovery in these processes requires thermal energy storage systems for closing the temporal gap between energy supply and demand. The ongoing digitalization in the field of industrial energy systems enables modern applications like digital twins to increase the efficiency of energy intensive processes. This paper presents the implementation of a five-dimensional digital twin platform for a packed bed thermal energy storage test rig. The five-dimensional digital twin platform allows the development of services and applications in interdisciplinary teams and facilitates their interaction on a standardized platform. By that the digital twin helps to make modern industrial energy systems more efficient.

Abstract

Co-gasification technology provides a feasible solution for the energetic valorization of various types of biomass feedstocks, especially those not directly applicable for gasification owing to their low-calorific values or high ash content. Numerical modelling is a promising approach to evaluate the performance and analyze the conversion processes inside the gasifier, but the complexity of cogasification technology has put forward challenges to the model formulation. This paper established the Multiple Thermally Thick Particle (MTTP) model for simulating the co-gasification process. MTTP model could not only calculate the individual conversion processes of different fuels, but also simultaneously reflect the characteristics of thermally thick particles and the interactions between different fuels through sub-grid models for the solid phase. Experimental results of a downdraft fixed-bed co-gasification from literature were adopted for model validation. The modelling results from the MTTP model are in good agreement with the measured values of temperature and syngas composition upon changing the co-gasification ratio (CGR). Further analysis of the weight-loss process of different fuel particles and the corresponding intraparticle temperature distribution have confirmed the different conversion characteristics and interactions between different fuels during co-gasification process.

Abstract

Liquid hydrocarbons made from crude oil serve many functions: (1) a dense, easy-to-store, easy-to-transport energy source, (2) a method for daily-to-seasonal energy storage, (3) a chemical feedstock, (4) a chemical reducing agent and (5) a method to enhance high-temperature heat transfer in many furnaces and industrial processes. There are multiple methods to produce and use liquid hydrocarbons without increasing atmospheric carbon dioxide levels including (1) negative carbon emissions to balance carbon dioxide releases from burning crude-oil products and (2) producing liquid hydrocarbons from non- fossil feedstocks such as carbon dioxide or biomass. Understanding liquid hydrocarbon demand is the starting point in assessing options for producing and using liquid hydrocarbons without increasing atmospheric carbon dioxide levels. Our assessment is that U.S. demand for liquid hydrocarbons is unlikely to go below the equivalent of 10 million barrels per day of crude oil. The costs to replace liquid hydrocarbons increases rapidly at lower liquid hydrocarbon consumption rates. Hydrocarbon biofuels from cellulosic feedstocks can meet such demands but options based on more limited feedstocks (bio oils, sugars, etc.) can’t meet such demands.